Water recovery, primarily in the cathode side, of a proton exchange membrane fuel cell

Abstract

A fuel cell or fuel cell stack has a proton exchange membrane or other electrolyte, and appropriate inlets and outlets for cathode and anode sides of the fuel cell. Dryers are connected to the cathode inlet and cathode outlet in such a manner as to enable one dryer to recover moisture from an exhausted oxidant stream while the other dryer is humidifying an incoming stream. Optionally, a dryer arrangement can be provided for recovering moisture on the anode or fuel side of the fuel cell.

What is claimed is:  
     
       1. A fuel cell comprising: an anode with a respective anode inlet and an anode outlet for a fuel gas; a cathode with a respective cathode inlet for an incoming oxidant gas stream and a cathode outlet for an outgoing oxidant gas stream; an electrolyte between the anode and the cathode; first and second dryers; and valve means connecting the first and second dryers to the cathode inlet and the cathode outlet, whereby, in use, the first dryer can be connected to one of the cathode inlet and the cathode outlet and the second dryer can be connected to the other of the cathode inlet and the cathode outlet, wherein the connections of the dryers can be periodically switched between the cathode inlet and the cathode outlet, whereby one dryer recovers moisture from the outgoing oxidant gas stream and the other dryer humidifies the incoming oxidant gas stream. 
     
     
       2. A fuel cell as claimed in  claim 1 , which includes an inlet three-way valve having a common port connected to the cathode inlet and first and second branch ports, connected to the first and second dryers respectively, and an outlet three-way valve having a common port connected to the cathode outlet and having first and second branch ports connected to the first and second dryers respectively, each of the inlet and outlet three-way valves being switchable to connect one of the branch ports thereof to the common port thereof and to close off the other of the branch ports, and wherein the inlet and outlet three-way valves are interconnected, whereby when the inlet three-way valve provides communication between the first branch port thereof to the common port thereof, the outlet three-way valve provides communication between the second branch port thereof and the common port thereof, and when the first three-way valve provides communication between the second branch port thereof and the common port thereof, the second three-way valve provides communication between the first branch port thereof and the common port thereof. 
     
     
       3. A fuel cell as claimed in  claim 2 , which includes a pump provided between the inlet three-way valve and the cathode inlet, for displacing the incoming oxidant gas stream into the fuel cell. 
     
     
       4. A fuel cell as claimed in  claim 3 , which includes a plurality of fuel cells configured as a fuel cell stack, wherein the cathode inlet and outlet are connected to respective inlet and outlet manifolds connected to each of the fuel cells. 
     
     
       5. A fuel cell as claimed in  claim 1 ,  2 ,  3  or  4 , which includes a water separator provided between the cathode outlet and the second three-way valve for separating water droplets from the outgoing oxidant gas stream. 
     
     
       6. A fuel cell as claimed in  claim 1 ,  2  or  3  wherein the electrolyte comprises a proton exchange membrane. 
     
     
       7. A fuel cell as claimed in  claim 4 , wherein the electrolyte comprises a proton exchange membrane. 
     
     
       8. A fuel cell as claimed in  claim 1 , which is adapted for use with a fuel gas and which includes: a recirculation conduit including a pump connected between the anode inlet and the anode outlet; and a water separator provided in the recirculation conduit, between the anode outlet and the pump, for separating water from the fuel gas exiting the anode; and a main fuel inlet comprising a first fuel inlet connected to the recirculation conduit, for supply of the fuel gas. 
     
     
       9. A fuel cell as claimed in  claim 8 , which includes a branch conduit connected to the recirculation conduit and a dryer in the branch conduit, the branch conduit including a vent outlet. 
     
     
       10. A fuel cell as claimed in  claim 9 , which includes a shut-off valve in the branch conduit, upstream of the dryer for controlling flow of fuel gas to the dryer, the shut-off valve being operable to effect purge cycles, in use, to purge accumulated and unwanted gases from the anode. 
     
     
       11. A fuel cell as claimed in  claim 8 , which includes a dryer in the recirculation conduit, downstream from the water separator. 
     
     
       12. A fuel cell as claimed in  claim 11 , which includes a branch conduit connected to the recirculation conduit, downstream from the dryer and including a shut-off valve. 
     
     
       13. A fuel cell as claimed in  claim 9  or  12 , wherein the branch conduit is connected to the recirculation conduit upstream from the pump. 
     
     
       14. A fuel cell as claimed in  claim 10 , which includes a second fuel inlet connected to the branch conduit between the dryer and the vent outlet, and a second shut-off valve in the branch conduit between the second fuel inlet and the vent outlet, for effecting reverse flow of the fuel gas through the dryer to recharge the dryer and to recover moisture therefrom. 
     
     
       15. A fuel cell as claimed in  claim 14 , which includes a fuel control valve in the second fuel inlet, for control thereof. 
     
     
       16. A method of recovering moisture from an outgoing oxidant stream and humidifying an incoming oxidant stream in a fuel cell, which comprises an anode to which fuel is supplied and a cathode through which an oxidant stream passes and an electrolyte between the anode and the cathode, the method comprising the steps of: 
       (i) passing an outgoing oxidant stream from the cathode through a first dryer to recover moisture therefrom;  
       (ii) passing an incoming oxidant stream through a second dryer to humidify the incoming stream with moisture previously trapped in the second dryer; and  
       (iii) periodically switching the incoming and outgoing streams between the first and second dryers whereby each of the dryers alternately effect each of steps (i) and (ii).